A kind of water-based composite passivation solution for galvanized steel sheet and preparation method thereof

Abstract

The invention relates to a water-based composite chromium-free passivation solution for a galvanized steel plate. The passivation solution contains 10-30g / L of sodium molybdate, 0-10g / L of sodium phosphate, 5-10g / L of organic phosphoric acid, 1-10g / L of fluotitanic acid, 5-15g / L of a silane coupling agent, 5-20g / L of sodium metasilicate, 0.1-1% of a wetting dispersant and the balance of deionized water. The passivation solution provided by the invention consists of an organic phosphoric acid-molybdate system in match with the modified hydrolysis type silane coupling agent and a nano-inorganic filler, does not contain a chromate and is in line with ROHS requirements; the passivation and drying curing time is short, the degree of stability is high, the quality of a film layer is good, the white rust area in a 72h salt fog test does not exceed 5%, the cost is relatively low, a passivation process device does not need to be changed, and continuous passivation can be realized by using a hexavalent chromium passivation device in early period.

Description

technical field [0001] The invention belongs to the technical field of hot-dip plating, and in particular relates to a water-based composite passivation solution for galvanized steel sheets and a preparation method thereof. Background technique [0002] At present, from the viewpoint of ensuring corrosion resistance, the surface of a coated steel sheet is often galvanized. Steel is usually passivated after electro-galvanizing or hot-dip galvanizing to prevent white rust in a short period of time. Although the traditional chromate treatment film is a thin film, it has excellent corrosion resistance, but it contains a large amount of hexavalent chromium, which is seriously harmful to the human body and the environment; in order to make the passivation film meet the requirements of environmental protection and solve the pollution problem of hexavalent chromium, Abandoning the traditional chromic acid passivation process and developing and researching chromium-free passivation ...

AI Technical Summary

Problems solved by technology

[0003] The toxicity of trivalent chromium is only 1 / 100 of that of hexavalent chromium. Trivalent chromium passivation is a transitional technology. The passivation film is beautiful and has excellent corrosion resistance, but the passivation solution has poor stability, low service life, narrow allowable pH, The film layer has the disadvantage of no self-healing ability; and because most of the trivalent chromium passivation solutions need to add oxidants, improper formulation will make the film layer contain hexavalent chromium, so the trivalent chromium technology has been gradually eliminated by the chromium-free technology.

However, most of the existing chromium-free technologies must use roller coating to ensure the coating amount, and the drying and curing process is complicated

Therefore, it is not possible to use simple equipment such as the existing spray wringer during production, but it is necessary to invest in new equipment for the galvanizing production line.

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